1. Field of the Invention
The present invention relates to an electrophotographic organic photoreceptor, and more particularly, to a double-layered positively-charged organic photoreceptor.
2. Description of the Related Art
Double-layered positively-charged electrophotographic organic photoreceptors basically include an electroconductive support coated with an adhesive layer or a charge blocking layer, a charge transport layer, and a charge generating layer. An optional overcoat layer is formed on the charge generating layer, which has a small thickness, to protect it from wearing by attrition with toner or a cleaning blade.
An electrophotographic imaging process using such a double-layered positively-charged organic photoreceptor is as follows. After positively charging the surface of an organic photoreceptor, a laser beam irradiates a charge generating layer to generate positive and negative charges. Positive charges (holes) are injected into a charge transport layer by an electric field applied to the organic photoreceptor and migrate to an electroconductive support. The negative charges (electrons) migrate to the surface of the organic photoreceptor to neutralize surface charges. A surface potential varies by exposure, so that a latent image is formed in an exposed region. Then, this latent image is developed with toner.
Compared with single-layered organic photoreceptors requiring complex electrical properties for a single layer, double-layered positively-charged organic photoreceptors including two layers responsible for different functions may more easily control electrical properties, such as charge potential and exposure potential. Since a stable electric field may be applied to the thin surface layers of a double-layered positively-charged organic photoreceptor, the photoreceptor can retain a larger amount of charge at a given field strength and develop images with a larger amount of toner.
In such a double-layered positively-charged organic photoreceptor, a charge transport layer coated on an electroconductive support generally contains a charge transport material and a polycarbonate-based binder resin. However, due to ineffective adhesion of polycarbonates to the electroconductive support, the organic photorecepting layer is likely separated from the electroconductive support by attrition with toner, rollers, and a cleaning blade. Moreover, this problem becomes more serious when wet developing is applied to the organic photoreceptor because a hydrocarbon-based solvent of a wet developer permeates into the organic photoreceptor and weakens the binding strength of a resin used as a binder.
To resolve these problems, using an anodized electroconductive support, coating the electroconductive support with an additional adhesive layer for adhesion enhancement, or using a charge blocking layer, which also prevents charge injection from the electroconductive support, has been suggested.
However, both cases raise the price of the organic photoreceptor due to additional anodizing or coating. In addition, a problem of contaminating a charge transport layer coating solution, which becomes more serious with repeated coatings, arises with the latter suggestion, because the adhesive layer dissolves in and mixes with a solvent of the charge transport layer coating solution applied to the surface of the adhesive layer.